Chapter 2.3, Problem 2.2P

Interpretation Introduction

Interpretation:

The arrows which violate either one of the two commandments has to be determined.

Concept Introduction:

Resonance is a way of representing a structure which has the same connectivity but the electrons are distributed differently in the structures.  In resonance structure drawing, the electrons are considered as clouds.  These electron clouds very often spread across a large region of a molecule.  Curved arrows are the best way to represent the resonance structures.  With the help of curved arrows, the movement of electron can be shown.  Every curved arrow comprises of a head and tail.  Tail shows the place from where electrons are coming and head shown the place where electrons are going.  It is not the electrons migrating as such.  We treat the electrons to migrate to draw all resonance structures.  For drawing curved arrows, two important commandments has to be always followed.  They are,

• Thou shall not break a single bond.
• Thou shall not exceed an octet for second-row elements ($\text{C,}\text{N,}\text{O,}\text{F}$).

Resonance structures should have the same connectivity.  Hence, breaking of a single bond is not at all allowed.

Second-row elements should never exceed the octet.  This is because they have only four orbitals in their valence shell.  The sum of bonds and the lone pairs for second row elements should never exceed the number four.